Add rndc dnssec -rollover command

Add rndc dnssec -rollover command

This command is similar in arguments as -checkds so refactor the
'named_server_dnssec' function accordingly.  The only difference
are that:

- It does not take a "publish" or "withdrawn" argument.
- It requires the key id to be set (add a check to make sure).

Add tests that will trigger rollover immediately and one that
schedules a test in the future.